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Comparisons of Beta‐Adrenergic Blocking Properties of S‐ and R‐Timolol in Humans
Author(s) -
Rotmensch Heschi H.,
Vlasses Peter H.,
Feinberg Jerry A.,
Abrams William B.,
Ferguson Roger K.
Publication year - 1993
Publication title -
the journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.92
H-Index - 116
eISSN - 1552-4604
pISSN - 0091-2700
DOI - 10.1002/j.1552-4604.1993.tb04701.x
Subject(s) - timolol , blocking (statistics) , beta (programming language) , adrenergic beta antagonists , pharmacology , adrenergic , adrenergic receptor , medicine , anesthesia , propranolol , intraocular pressure , mathematics , ophthalmology , computer science , receptor , statistics , programming language
In animals, the R‐enantiomer of timolol causes a significant reduction in intraocular pressure but had only 1/80 the activity of the S‐enantiomer at extraocular receptors. The beta 1 ‐ and beta 2 ‐adrenoceptor blocking properties of orally administered R‐and S‐timolol were compared in a double‐blind placebo controlled trial in two groups of healthy men. Each subject in group A (n = 6) received placebo, 1 and 3 mg S‐timolol and 25 and 75 mg R‐timolol in random order, group B (n = 5) received placebo, 0.5, and 1 mg S‐timolol and 3 and 10 mg R‐timolol. In both groups, R‐and S‐timolol comparably inhibited isoproterenol‐induced increases in heart rate (P < .05), forearm blood flow (P < .05, except at 3 μg/minute of isoproterenol after the R‐doses in group B), and finger tremor (P < .05) in comparison with placebo. The findings for the R‐enantiomer in this study were unexpected based on the animal studies and previous studies that demonstrated marked differences in beta blocking effects of other beta‐blockers in which the R‐enantiomers were less inhibitory.